Re[2]: impedance across ground plane

Barry Ma ([email protected])
Thu, 22 Feb 1996 13:00:17 -0500

Hi Gentlemen,

Please allow me to present an alternative viewpoint and correct me.

What does "good ground" mean? The definition of "good GND" should be
"a low-impedance return path back to the source." If some unwanted
current at low frequency (say, 50 Hz) can get back to it's source easily
through earth GND, let's secure the connection from the unit to the
earth. If EMI at RF comes from a chip inside the unit, why do we have to
reduce the impedance at 3 GHz to earth ground through GND plane of PCB and


______________________________ Reply Separator _________________________________
Subject: Re: impedance across ground plane
Author: Nirmal Jain <[email protected]> at INTERNET
Date: 2/16/96 11:34 AM

Hi Joe,

The impedance across the gnd plane in high speed design
is due to the inductances and the resistances offered to different
current paths in the plane.

To figure out this impedance you can model your plane
using modeling tools. To effectively model your pcb plane you might
need switching and some placement information.

You can find more information on plane modeling in papers by davidson
(from ibm) I think or in any paper disucssing ground bounce or ssn.

Hope it helps.


>Can anyone help this fellow?
>----- Begin Included Message -----
>To: [email protected]
>Subject: impedance across ground plane
>fellow technetters,
>We are searching for information on the impedance across the ground
>plane on a pcb. We have some harmonics near 3 Ghz, and would like to
>see if we can reduce the impedance to earth ground through our pcbs,
>and backplanes.
>If anyone knows of some sources where we can look up information
>please forward.
>thanks in advance
>Joe Zdybowicz
>CAD Engineer
>FORE Systems
>174 Thorn Hill Road
>Warrendale PA 15086
>email: [email protected]
>----- End Included Message -----

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